As a method of determining a location of a terminal device, there is a method utilizing electromagnetic waves and sound waves, for example. FIG. 20 is a view illustrating this method utilizing electromagnetic waves and sound waves.
Beacons 200-1 to 200-3 periodically transmit electromagnetic waves and sound waves at the same time. A terminal device 100 receives an electromagnetic wave (EM1) transmitted from the beacon 200-1, for example, and obtains location information of the beacon 200-1 from information included in the electromagnetic wave (EM1). Then, the terminal device 100 receives a sound wave (S1) and calculates a distance to the beacon 200-1 based on a difference in arrival time between the electromagnetic wave (EM1) and the sound wave (S1). The distance to the beacon 200-1 may be determined, for example, by multiplying a speed difference between an electromagnetic wave and a sound wave by the arrival time difference. In the same way, the terminal device 100 obtains location information of the beacons 200-2, 200-3, and calculates distances to the beacons 200-2, 200-3. Having obtained the location information and the distances of the three beacons, the terminal device 100 calculates the location information of the terminal device 100 by trilateration.
In a method utilizing GPS, for example, a terminal device within doors is incapable of a location determination since radio waves from a GPS satellite do not reach indoors. In contrast, in the method utilizing electromagnetic waves and sound waves, a terminal device within doors is capable of a location determination since beacons configured to transmit the electromagnetic waves and the sound waves are installed within doors.
Moreover, in the method utilizing electromagnetic waves and sound waves, installation cost of equipment may be reduced since the method uses no location server or no synchronization server. In addition, this method utilizing arrival time differences of electromagnetic waves and sound waves is capable of calculating the distances to beacons without using received power strengths of the electromagnetic waves and the sound waves, and therefore achieves improvements in the accuracy of calculation of distances between a terminal device and beacons, and also in the accuracy of location information determination of the terminal device. Meanwhile, this method utilizing arrival time differences of electromagnetic waves and sound waves is under a restriction on the number of installable beacons such that the maximum number of installable beacons is 22, for example.
The followings are examples of techniques for the method utilizing electromagnetic waves and sound waves.
Specifically, one of the techniques is for an autonomous ultrasonic indoor positioning system in which a structured ultrasonic transmitter including a single RF transmitter and multiple ultrasonic transmitters transmits ultrasonic waves at regular intervals, and a reception device calculates the location of the reception device based on differences between reception times of the ultrasonic waves at the reception device.
This technique is considered to enable provision of a highly-accurate low-cost indoor positioning system.
Another technique is for a distance measurement method in which two sound sources placed at two locations at different heights transmit electromagnetic waves and sound waves at the same time, and a terminal device calculates the distances to the two sound sources from the received waves, and calculates the horizontal distance to the sound sources in accordance with the Pythagorean theorem.
This technique is considered to enable measurement of the horizontal distance to sound sources even in a location with a large difference in height and poor visibility.
The related techniques are disclosed in, for example, Japanese Laid-open Patent Publication Nos. 2009-288245 and 10-48309.